Box stitching machines have been in existence for some time which include a stitching head for applying wire stitches to overlapping portions of a box blank passing therebeneath and conveying means for incrementally advancing the box blank past the stitching head. Conventionally, such conveying means have taken the form of cooperating pull rollers which sandwich the box blank therebetween and advance the same through the machine in response to the driving rotation thereof.
At startup, the pull rollers operate at a continuous high rate of speed to initially convey the box blank from the input side of the machine toward the stitching station defined by the stitching head. When the box blank reaches a preselected position with respect to the stitching head, appropriate sensing means (in the form of a mechanical sensing finger or a photocell arrangement) detects the leading edge of the box blank to energize a timer which generates a signal after a fixed interval which starts the operation of the stitching head. The stitching head then begins to apply the first stitch to the box blank positioned therebeneath.
Simultaneously with the operation of the stitching head, a signal is generated to stop the aforementioned pull rollers holding the box blank stationary beneath the head when the first stitch is applied thereto. After the completion of the first stitch, and after the stitch driving means associated with the head has been lifted from the box blank, another signal is generated to start the pull rollers moving again to advance the blank a preselected distance whereupon the pull rollers are again stopped to halt the movement of the box blank to await the application of the next stitch being applied by the now continuously operating stitching head. This cycle of stop and start movement of the box blank and the application of a stitch at the stop or dwell period of the box blank motion continues until a preselected number of stitches have been applied or a predetermined portion of the blank has been stitched. At this point the stitching head is de-energized and pull rollers returned to their earlier mode of continuous operation to rapidly eject the box blank from the stitching machine. In my priorly issued U.S. Pat. No. 3,664,564, an electronically controlled stitching machine is disclosed which places a predetermined number of stitches in a box with predetermined spacing therebetween. It has been found that when heavy boxes have been stitched, either with my above-mentioned machine, or any of the other prior art machines, variations in spacing occur between the stitches.
In my prior U.S. Pat. No. 3,758,015, I disclosed an electronically controlled stitching machine in which the spacing variation of stitches resulting from heavy boxes was overcome by providing a photocell which detected a last stitch position and placed a stitch at that last position without regard to the previous stitch spacing. This system overcame the problem encountered when the last stitch was not sufficiently close to the end of the box to ensure proper fastening. However, an uneven pattern of stitching resulted therefrom.
Therefore, it is an object of this invention to provide a new and improved box stitching machine.
It is another object of this invention to provide a box stitching machine which maintains even spacing between stitches regardless of the weight of boxes being stitched.